1. Field of the Invention
This invention relates in general to inertial navigators, and in particular to inertial navigators where it is desired to "correct" the system for key error sources in order to provide improved directional accuracy and improved navigational performance. 2. The Description of the Prior Art
In the prior art, inertial navigators have been corrected in flight utilizing external navigation aid(s) (such as the Global Positioning System, GPS) and an optimal estimation filter. We use the term "correct" to mean the alignment and initialization of the system and the calibration (correction) of the various inertial navigator error sources. Such a technique suffers from the fact that many inertial navigator error sources are unobservable and thus uncorrectable by the techniques of the prior art. For example, it is not possible to distinguish between an accelerometer bias error and a level misalignment error, nor between an "East" Gyro Drift Rate and an azimuth misalignment error.
The present invention makes it possible to align and initialize the system "at rest" on the ground and/or periodically in-flight and to insure that the system is devoid of the effects of key error sources. The key error sources are the ones that provide for degraded directional accuracy and position errors that increase with time (specifically, level-axes drift rates, azimuth misalignment error and azimuth-axis drift rate).
The prior art, as practiced, is not adequate to accomplish this specific purpose. The present invention achieves this specific purpose and as such provides the techniques required to align and initialize the system "at rest" on the ground and/or periodically in-flight and to ensure that the system is devoid of the effects of the above key error sources.